The present invention relates generally to dosing lamp fill material in lamps. More specifically, the present invention relates to dosing small quantities of halogens in high intensity discharge (xe2x80x9cHIDxe2x80x9d) lamps.
HID lamps with a vaporizable lamp fill have found widespread use in lighting large outdoor and indoor areas such as athletic stadiums, gymnasiums, warehouses, parking facilities, and the like, because of the relatively high efficiency, compact size, and low maintenance of HID lamps when compared to other lamp types. HID lamps have also been developed as point sources. In many applications, it is advantageous to lamp operation to provide a small amount of a halogen in the arc tube of HID lamps. In other applications, it may be advantageous to provide a small quantity of one or more metals in the arc tube of HID lamps.
For example, ultra high pressure mercury lamps operate with mercury pressures of 100 atmospheres and higher and have been found to be good point sources for projection and optical systems. One disadvantage of such lamps is a reduced operating life resulting from the blackening of the walls of the arc tube due to deposition of tungsten from the lamp electrodes on the arc tube wall. It is known that small quantities of a halogen dosed into the arc tube of the lamp reduces the blackening of the wall of the arc tube and thus extends the life of the lamp. Typically, chlorine, bromine, or iodine is dosed into ultra high pressure mercury lamps, however, bromine has been favored in most applications. The quantity of halogen dosed in these lamps is typically less than 0.1 mg and may be less than 0.1 xcexcg. For example, U.S. Pat. No. 5,497,049 to Fischer discloses an ultra high pressure mercury lamp having a dose of bromine of less than 0.1 xcexcg.
There remains the practical question of how to dose such small quantities of a halogen into the arc tube of a HID lamp. One known method is to add an appropriate quantity of halogen gas to the inert fill gas of the lamp. In the example of providing bromine in an ultra high pressure mercury lamp, the bromine in the form of Br2 may be added to the argon fill gas. However, it is difficult to control the Br2 concentration in the fill gas and the Br2 may be absorbed on the surfaces of the gas delivery system gas or react with system components. Thus precise small quantities of bromine are difficult to dose into lamps using this method.
Another known method of dosing such small quantities of bromine in a HID lamp includes adding methylene bromide (CH2Br2) vapor to the argon fill gas of the lamp as disclosed in U.S. Pat. No. 5,109,181 to Fischer et al. However, it is difficult to control the concentration of the vapor in argon in this method. Further, hydrogen contamination in the lamp is possible.
Yet another known approach to dosing such small quantities of bromine into a lamp includes the formation of lamp fill particles formed from mercuric bromide (HgBr2). However, it is very difficult to fabricate and handle a sphere having quantities of halide as low as 0.1 xcexcg. Even larger spheres having as much as 0.05 mg of halide are difficult to dose into lamps because of the small size of the spheres. The spheres are also difficult to handle and dose because of static electricity.
Thus there remains a need for a method of dosing small quantities of a halogen in a HID lamp in an easily fabricated and dosed lamp fill material.
Accordingly, it is an object of the present invention to obviate the deficiencies of the known prior art and to provide a novel lamp fill material.
It is another object of the present invention to provide a novel particle suitable for introducing small quantities of a halogen into a HID lamp.
It is yet another object of the present invention to obviate the deficiencies of the known prior art and to provide a novel method of dosing a lamp.
It is still another object of the present invention to provide a novel method of dosing a HID lamp with small quantities of a halogen in a solid lamp fill particle.
It is a further object of the present invention to provide a method of dosing a lamp which reduces the introduction of impurities into the lamp.
It is yet a further object of the present invention to provide a novel lamp fill material for introducing a metal and metal halide into a HID lamp.
It is still a further object of the present invention to provide a novel method of dosing a HID lamp with small quantities of one or more metals and a metal halide.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.